Recovery of alcohols from direct hydration of olefins



Aug. 11, 1953 E wfcARRlER RECOVERY OF ALCOHOLS FROM DIRECT HYDRATION OF'OLEFINS Filed July 19, 1949 Patented ug. 11, Q

RECOVERY or ALCOHoLs FROM DIRECT HYDRATION 0F OLEFINs E. WendellCarrier, Cranford, N. J., assignor to Standard Oil Development Company,a corporation oi' Delaware Application July 19, 1949, Serial No. 105,566

8 Claims.

This invention relates to an improved process ior the recovery cialcohol obtained by the direct hydration of olefins. The invention isspecically concerned with the recovery of alcohol substantially free ofether and dissolved hydrocarbons in a single operation from the olenhydration products. More particularly the invention is concerned Withthe recovery of alcohol free of ether from oleiin hydration products bysubmitting the Vaporous product under the conversion conditions oftemperature and pressure to an extractive distillation operation inWhich the ether is removed overhead together with all unreactedhydrocarbons and in which the alcohol substantially free of ether isrecovered as an aqueous solution as bottoms from the extractivedistillation zone.

In the direct synthesis of ethanol from ethylene and Water at hightemperatures and pressures, employing aqueous acid catalysts either asliquids or as liquids supported on an inert carrier or employing solidcatalysts as such, Wherein the ethanol formed is obtained as a complexvapor mixture with the unreacted portions of the feed gases containingalso inert hydrocarbon diluents and appreciable quantities of diethylether, which is an undesirable by-product, a very important problem inthe devel-opment of an economic process is enicient recovery of theethanol from the Vapor mixture discharged by the reactor. The recoverystep is important due to the necessity to recycle continuously largeamounts of unreacted ethylene, and usually diethyl ether, to the reactorin order to obtain practical utilization of the raw material, as Well asldue to the fact that the ethanol must nally be produced in commerciallypure form to be sold favorably.

All known processes prior to U. S. 2,142,036 teach that regardless ofthe manner in which the hydration reaction is conducted, or the meansused t0 recover the heat in the vapors from the reaction zone, the onlyWay in which the products of reaction may be recovered is to cool thevapor mixture to a relatively low temperature where condensation of asubstantial part of the alcohol and ether products takes place, togetherWith condensation of most of the residual Water vap-or accompanying thereaction products, U. S. 2,142,035 teaches that alcohols may berecovered from the complex vapor mixture from the reaction zone byscrubbing With Water under substantially the same high pressure andtemperature conditions prevailing in the reactor. The

scrubbing Water is preheated and regulated to bons.

such temperature that the Washed gases are saturated with steam in thedesired ratio to olefin for recycling to the reaction zone. In thismanner the unreacted gases are purified of the products of reactionWithout appreciable cooling and Without condensation of the residualWater vapor. The dilute aqueous alcohol solution from the scrubber (orabsorber) is continuously distilled in order to remove the alcohol fromthe major portion of the Water at substantially the 'temperature of thescrubbing system, so that the alcohol-free water can be recycled to thescrubber With negligible heat loss. However, no mention is made in U. S.2,142,036 of the presence of undesirable quantities of ether generallyaccompanying the alcohol formed by the hydration .of olens underpractically al1 reaction conditions'. Neither is mention made in U. S.2,142,036 that the water containing the recovered alcohol at the bottomof the scrubber will also contain some dissolved unreacted olefin andother low `boiling hydrocarbons accompanying the original olefin feed tothe reaction zone.

The process of this invention represents an improvement of the processof U. S. 2,142,036. According to this invention it is proposed torecover alcohol iree oi ether and hydrocarbons from the vaporousproducts of the direct hydration reaction by submitting the vaporousproduct at substantially the high temperaturev and pressure conditionsof the hydration reaction to a Water extractive distillation operati-on.In this manner practically all the ether is removed from the hydrationproduct as an overhead vapor stream together with all unreactedhydrocar- The ether and unreacted hydrocarbons are saturated with steamand are returned to the hydration reactor. The water entering at the topof the extractive distillation column is preheated and regulated to theproper temperature to saturate the ether and hydrocarbons recycled tothe reactor With steam in just the desired ratio. Usually the desiredquantity of steam to be recycled to the reactor is the same as that inthe vaporous product from the reactor. Dilute aqueous alcoholpractically free of ether and hydrocarbons is obtained as bottoms fromthe extractive distillation zone. The bottoms are continuously distilledWithout appreciable reduction of temperature to recover the dissolvedalcohol from the major portion of the Water and the water is returnedwithout major heat loss but with temperature adjustment to the top oflthe Water extractive distillation zone. The Water extractivedistillation column may be operated with or without external reflux.External reflux is usually not required but may be obtained by addingsmall quantities of ether to the water returned to the top of theextractive distillation column.

The process of this invention has the advantage that extra fractionationequipment and energy are not expended further on' in the alcorhol plantto remove ether and hydrocarbons to the high degree necessary tomanufacture commercially pure alcohol, particularly ethanol andisopropanol. Furthermore, since it is usually desirable to recycle therecovered ether to the reaction zone in order to suppressI itsformation, essentially all of the ether in the reactor vapors' are leftin the efliuent gases from the Water extractive distillation Zone fordirect recycling along with unreacted olefins saturated with stream inthe desired ratio.

The conditions employed in the direct hydration reaction are thoseconditions which arewell known in the art. Temperatures in the vicinityof 150-375l C., preferably 20G-250 C., and pressures from atmospheric4pressure up to 3000 p. s. i. g. or higher areA employed. Within thepreferred temperature rangev a pressure of 509- 1000 p. s, i. g. is thepreferred pressure. The catalyst employed in the'reaction'is anacid-type catalyst. It may be-an aqueous catalyst such as aqueoussulfuric acid or phosphoric acid, preferably dilute sulfuric acid orphosphoric acid, or the catalyst may bein solid form, for" example,phosphoric acid on a suitable carrier such as alumina. The solidcatalystl may be employed with the various promoters welll known in theart. If an aqueous catalyst is used, it is usually advantageous torecycle enough steam together' with the fresh feed water-added to thereactor to just saturate the vaporous product from the reactor atA thetemperature and pressure maintained for hydration. In this manner thecatalyst concentration isl kept constant.

The attached drawing illustrates in diagrammatical view one arrangementof apparatus for carrying out the present invention:

Referring to the drawing, an olefin-containing gas is admitted to thesystem through line l. After compression it is'adinixed with recycle gasfrom the extractive distillation column 'I in the hydration reactionzoneV 3'. Feed water is pumped into reactor 3 through line 4 in anamount usually suicient to furnish the steam use-d up by the hydrationreactionbut insunlcient to saturate the eiiiuent vapors from thereactor. The temperature of the feed water is'ad'justed before admissionto the reaction zone in order to control the temperature of thecatalystY therein; Heat is evolved by the olefin hydration reactionwhich is absorbed by vaporization of the feed water and by its change insensible heat content in the reactor. In thereaction` zone the olefinand steam react in the presence of the catalyst Within the temperatureand pressure ranges previously mentioned to form alcohol and, inaddition, more orless considerable quantities of ether; The alcohol,ether, steam, unconverted olefin and other hydrocarbon rgases leave thereaction zone in the vapor phase via line 5. The total reactor effluentwithout condensation is introduced at an intermediate point into theextractive distillationzonerl, where the temperature and pressure issubstantially the same as in the reaction Zone, that is, at temperaturesbetween150 and.375 C'., andat pressures from 500 to. 3G00p. s. i. g.However, it is usually necessary to add small quantities of heat to thereactor vapors, as in superheater 6, before they enter the extractivedistillation zone 1. Unless the temperature of 'the reactor vapors isincreased slightly (or alternatively their pressure decreased), it isgenerally impracticable to obtain the desired conditions; in thestripping section of the extractive distillation zone, i. e., below thefeed point. Under some conditions which can be selected for the reactionzone, it is feasible to operate the intermediate feed point of theextractive distillation column at almost exactly the same temperatureand pressure as in the reactor.

Water is' fed-to the extractive distillation zone 1 in considerablequantities via line 8. The water is fed to the top or near the top ofthe column, but always above its intermediate feed point; To obtain thedesired separation of ether and hydrocarbons from` the alcohol, themixture is subjected to continuous fractional distillation in Zone 7'.The water introduced in suihciently large quantitiesat the upper part ofzone I effectively enhances the relative volatilities ofi the ether andhydrocarbons with respect to alcohol and Water so that essentially noneofthe ether and hydrocarbons isk lef-t in the dilute alcohol solution atthe bottom of the stripping section of zone '1. For continuous efficientoperation, Water must be added continuously.V near the top of the columnwhile the complex crude alcohol vapor mixture is continuously fedintovthe coll# umn at a lower point and while suicient heat, usually in theform. of direct steam, is provided to effect distillation throughout'.the column. A large proportion of the vapor-sof the crudealcoholcomponents introduced Ya'sfeed stream pass upwardlyy through theabsorbing section of the extractive distillation zone, i. e., above thefeed point, in contact with the descending internal aqueous liquidreflux under equilibrium boiling and refluxing conditions. In thestrippingk sec; tion of zone 1 thev quantity ofvapor flowing up ward isusuallyimuch less-than in` the absorbing section due to the vapor feed,but these stripped vapors are likewisev in contact. with descendinginternal aqueous liquid reflux under equilibrium boiling conditions. Dueto the'fact thatl water very much in excess of the amount of Waterdistilled overhead with the ether and hydrocarbons enteringwith the feedvapors, together with a small amount of alcohol which is. alsodistilled, is introduced near the top of the absorbing -section, thewater concentrationinthe. descending liquid throughout the column isconsiderably higher than the water concentration in the vapors incontact withtheliquidtin any part' of Zone 1. As previously mentioned,the-'temperature of the Water continuously fed nea-r the top of theabsorbing section is regulated externally, as in heater 9, so that thedistilled vapo'rs of ether, unreacted olefin, otherloW-boilingf'hyd'rocarbon impurities-in the olenfeed to thereactor and alittle alcohol vapor aresaturated with steam in just the rig-ht ratioyforV recycling tothe reaction Zone vial line' l2.

The complex vapor mixture just described which is-distilled from'the topof the'di'sti-l-lat-ien zone 7 leaves the column vialine lit, whencesitis split into two streams. -A-very small-'sides'tream is withdrawnthrough pressure reducing valve Ilv in order to purge the 1ow=boi1inghydrocarbons, such as methane andy ethane, which entered the system withthe fresh olefin-feed -to the reactor. Unless the.V small sidestrea-mpurge is taken, the low-boiling hydrocarbon impurities will accumulateto be an undesirably high proportion of the recycle stream. It may beadvisable to recover small quantities of alcohol and water, togetherwith some ether contained in the purge stream, by partially condensingthe bleed gas in a condenser (not shown on the drawing) under reducedtemperature conditions. The condensate so obtained may be pumped backinto the absorbing section of the extractive distillation zone l', or itmay be mixed with the relatively large quantity of water entering thecolumn in line 8. By far the larger part of the vapor mixture leavingthe top of the extractive distillation column in line I is recycledthrough line I2 by means of gas pressure booster I3 back to thehydration reaction zone 3. It is the purpose of this recycle operationto increase the conversion of oleiin feed in the system so that only asmall quantity of oleiin will be present in the bleed gas releasedthrough valve I I. Also by recycling in this manner essentially all ofthe ether appearing in the vaporcus product from the reactor, the oleiinconverted in reaction zone 3 is hydrated almost entirely to the desiredproduct which is alcohol.

The quantity of water required continuously at the top of the extractivedistillation zone 'I must usually be enough to absorb, while descendingthrough the column, in excess of 80% of the alcohol present in thevaporous product from the reactor. The quantity of water required forthis purpose will, of course, depend on the concentration of alcohol inthe vapor from the reactor. However, if suiicient water is led to theextractive distillation column to enhance the volatilities of ether andhydrocarbons relative to alcohol and water to the degree necessary toeliminate practically all ether and hydrocarbons from the dilute aqueousalcohol bottoms leaving the stripping section of i by line Irl,generally no more than of the alcohol available in the reactor vapors isleft unabsorbed to be recycled through line i2. rhe quantity of waterrequired to improve the relative volatilities to the extent desired forcomplete vaporizaticn of ether and dissolved hydrocarbons is such thatthe concentration of the homogeneous internal reiux is substantiallyabove a critical minimum in the range of 65-99.9 mol percent water,preferably 95-99 mol percent water.

On the other hand, if no more eifective equipment than a scrubber isemployed to remove the alcohol from the reactor vapors, as suggested inU. S. 2,142,036, when enough water is fed to absorb in excess of 80% ofthe alcohol present, the scrubber bottoms will be found to containbetween 0.01 and 0.1 mol of ether per mol of alcohol absorbed, dependingon the alcoholether ratio in the hydration product and the operatingconditions of the scrubber. The scrubber bottoms will also contain smallquantities of dissolved hydrocarbons. Inasmuch as alcohol products mustbe essentially etherand hydrocarbon-free for the majority of commercialuses, additional fractionation and stabilizing operations would berequired to produce satisfactory alcohol either before or after thedilute alcohol is concentrated by rectification.

Returning to the attached drawing, hot, dilute aqueous alcohol of highpurity containing only 0.001 mol or less of ether per mol of alcohol isremoved under pressure from the bottom of the extractive distillationzone l via line I4. Before entering the alcohol concentrating zone I6,vit is desirable to lower the pressure by means" of r'e`=- ducing valveI5. The pressure may be reduced to any value corresponding to thedistillation temperatures selected for fractionation of the alcohol incolumn I6. The temperatures employed in the alcohol still depend upon aneconomic balance between the cost of the equipment, which is thefunction of the number of plates (or packed height) and the diameter ofthe tower, and the cost of steam used for distillation vs. the cost offuel or steam required in Water heater 9. In still i6 a large part ofthe water is removed, and the concentrated alcohol vapors pass overheadto condenser I'.' from which liquid reux is removed for return to thestill, and from which the puriiied alcohol product is withdrawn. Ifstill Iii is heated by direct steam, as shown, the water removed fromthe alcohol will pass out from the bottom of the still in admixture withcondensed steam. Excess steam condensate may be removed from the systemthrough line I9, together with any traces of non-volatile irnpuritiessuch as entrained catalyst from the reaction Zone. The rest of the waterpassesgby means of pump 20 back through heater 9 in line 8, where thetemperature is again raised to a predetermined point for introductioninto the top of the extractive distillation zone l. Makeup water (vialine 2l) may be added in line 8 ahead of pump 20 if required.

The extractive distillation column 'l may be a packed tower, abubble-plate column, or other known type of device for obtainingintimate contact between liquid and vapor.

It is to be understood that the process of this invention is restrictedto the production of those aliphatic alcohols which are stable, and atleast partially miscible with water at the high temperatures andpressures employed. The invention is particularly applicable to thepurification of ethanol resulting from the direct hydration of ethylene,and to the purication of isopropanol produced in a similar manner frompropylene.

It is obvious that the operating conditions of the extractivedistillation zone will vary with the alcohol being produced in thereaction zone. However, the extractive distillation is carried out undertemperature and pressure conditions substantially similar to thoseprevailing in the hydration reaction Zone. The amount of water added tothe distillation column will vary with the nature of the alcohol beingproduced. Although the invention has been described employing water inthe distillation process, it is permissible to use water containingsmall amounts of salts such as sodium acetate, or acids such as sulfuricacid, or even alkalis such as sodium hydroxide.

What is claimed is:

1. A process for the production of an etherfree saturated monohydricalcohol by the direct hydration of an olefin which comprises reactingthe olefin with Water vapor in a reaction zone at a temperature of C. to375 C. and at a pressure in the range of 500 p. s. i. g. to 3000 p. s.i. g in the presence of an acid catalyst, removing from the reactionzone a gaseous product comprising alcohol, ether and unreacted oleflns,passing the gaseous product without reduction in temperature andpressure to an intermediate point of anextractive distillation zone,introducing suiiicient water to the extractive distillation zone at apoint substantially above the gaseous product feed point to maintain aninternal liquid reux having a water content of 6in- 99.9 mol per centbelow the point of addition of the water, distilling from the gaseousproduct under sub stantially the same temperature andpressure conditionsof the hydration reaction a vaporous mixture comprising ether, alcoholand unreacted olens which flows countercurrent to the descending aqueousreflux, and withdrawing an aqueous solution of alcohol substantiallyfree of ether from a lower portion of the extractive distillation zone.

2. A process for the production of an etherfree saturated monohydricalcohol by the direct hydration of an oleiln which comprises reactingthe olen with water vapor in a reaction zone at a temperature of 150 C.to 375 C. and at a pressure in the range of 500 p. s. i. g. to 3000 p.s. i. g. in the presence of an acid catalyst, removing from the reactionzone a gaseous product comprising alcohol, ether and unreacted olefins,passing the gaseous product without reduction in temperature andpressure to an intermediate point of an extractive distillation zone,introducing sufficient water to the extractive distillation zone at apoint substantially above the gaseous product feed point to maintain aninternal liquid reiiux having a water content of 635-999 mol per centbelow the point of addition of the water, distilling from the gaseousproduct under substantially the same temperature and pressure conditionsof the hydration reaction a vaporous mixture comprising ether, alcoholand unreacted olefins which ilows countercurrent to the descendingaqueous reflux, withdrawing an aqueous solution of alcohol substantiallyfree of ether from a lower portion of the extractive distillation :v

zone, removing a gaseous stream comprising ether, unreacted olen andwater vapor overhead from the extractive distillation zone and returningthe gaseous stream tothe reaction zone.

3. A process for the production of diethyl ether-free ethanol by thedirect hydration of ethylene which comprises reacting ethylene withwater vapor in a reaction zone at a temperature of 150 C. to 375 C. andat a pressure in the range of 500 p. s. i. g. to 3000 p. s. i. g. in thepresence of an acid catalyst, removing from the reaction zone a gaseousproduct comprising ethanol, diethyl ether and unreacted ethylene,passing the gaseous product without reduction in temperature andpressure to an intermediate i point of an extractive distillation zone,introducing sufficient water to the extractive distillation zone at apoint substantially above the gaseous product feed Ipoint to maintain aninternal liquid reflux having a water content of 65-99 mol per centbelow the point of addition of the water, distilling from the gaseousproduct under substantially the same temperature and pressure conditionsof the hydration reaction a vaporousy mixture comprising diethyl ether,ethanol and unreacted ethylene which ows countercurrent to thedescending aqueous reiiux, and withdrawing an aqueous solution ofethanol substantially free of diethyl ether from a lower portion of theextractive distillation zone.

4. A process for the production of diethyl ether-free ethanol by thedirect hydration of ethylene which comprises reacting ethylene withwater vapor in a reaction zone at a temperature of 200 C. to 250 C. andat a pressure of 500 to 1000 p. s. i. g. in the presence of an acidcatalyst, removing from the reaction zone a gaseous product comprisingethanol, diethyl ether and unreacted ethylene, passing the gaseousproduct without reduction in temperature and pressure Iii) to anintermediate point of an extractive distillation zone, introducingsufficient water to the extractive distillation zone at a pointsubstantially abovethe gaseous product feed point to maintain aninternal liquid reux having a water content of 65-99 mol per cent belowthe point of addition of the water, distilling from the gaseous productunder substantially the same temperature and pressure conditions of thehydration reaction a vaporous mixture comprising diethyl ether, ethanoland unreacted ethylene which ows countercurrent to the descendingaqueous reflux, withdrawing an aqueous solution of ethanol substantiallyfree of diethyl ether from a lower portion of the extractivedistillation zone, removing a gaseous stream comprising diethyl ether,unreacted ethylene and water Vapor overhead from the extractivedistillation zone and returningthe gaseous stream to the reaction zone.

5. A .process according toclaim- 4f in which the water content of theinternal liquid reux is 95-99 mol per cent.

6. A process for the production of isopropyl ether-free isopropanol bythe direct hydration oi propylene which comprises reacting propylenewith water vapor in a reaction zonel at a temperature of 200 C. to 250C. and at a pressure of 500 to 1000 p. s. i. g. in the presence of anacid catalyst, removing from the reaction zone a gaseous productcomprising isopropanol, isopropyl ether and unreacted propylene, passingthe gaseous product without reduction in tem perature and pressure to anintermediate point of an extractive distillation zone, introducing sur"-cient water to the extractive distillation zone at a point substantiallyabove the gaseous product feed point tomaintain an internal liquidreiiux having a water content of 70-99 mol per cent below the point ofaddition of the water, distilling from the gaseous product undersubstantially the same temperature and pressure conditions of thehydration reaction a vaporous mixture comprising isopropyl ether,isopropanol and unreacted propylene which flows countercurrent to thedescending aqueous reflux, and withdrawing an aqueous solution ofisopropanol substantially free of isopropyl ether from a lower portionof the extractive distillation zone.

7. A process for the production of isopropyl ether-free isopropanol bythe direct hydration of propylene which comprises reacting propylenewith water Vapor in a reaction zone at a temperature of 200 C. to 250 C.and at a pressure of 500 to 1000 p. s. i g. in the presence of an acidcatalyst, removing from the reactionA zone a gaseoous product comprisingisopropanol, isopropyl ether and unreacted propylene, passing thegaseous product without reduction in temperature and pressure to anintermediate point of an extractive distillation zone, introducingsufficient water to the extractive distillation Zone at a rpointsubstantially above the gaseous product feed point to maintain aninternal liquid reflux having a water content of '7D-99 mol per centbelow the point of addition of the water, distilling from the gaseousproduct under substantially the same temperature and pressure conditionsof the hydration reaction a vaporous mixture comprising isopropyl ether,isopropanol and unreacted propylene which flows countercurrent to thedescending aqueous reflux, withdrawing an aqueous solution ofisopropanol substantially free of isopropyl ether from a lower portionof the extractive distillation zone, removing a gaseous streamcomprising isopropyl ether, unreacted 9 propylene and Water vaporoverhead from the Number extractive distillation zone and returning the2,142,036 gaseous stream to the reaction zone. 2,290,636 8. A processaccording to claim 7 in which 2,313,196 the water content of theinternal liquid reflux 5 is 95-99 mol per cent.

Number E. WENDELL CARRIER. 527,316

Name Date Bump May 11, 1937 Number Name Date Rowland et al. Dec. 27,1938 Deanesly July 21, 1942 Guinot Mar. 9, 1943 FOREIGN PATENTS CountryDate Great Britain Oct. 7, 1940

1. A PROCESS FOR THE PRODUCTION OF AN ETHERFREE SATURATED MONOHYDRICALCOHOL BY THE DIRECT HYDRATION OF AN OLEFIN WHICH COMPRISES REACTINGTHE OLEFIN WITH WATER VAPOR IN A REACTION ZONE AT A TEMPERATURE OF 150*C. TO 375*C. AND AT A PRESSURE IN THE RANGE OF 500 P. S. I. G. TO 3000P. S. I. G IN THE PRESENCE OF AN ACID CATALYST, REMOVING FROM THEREACTION ZONE A GASEOUS PRODUCT COMPRISING ALCOHOL, ETHER AND UNREACTEDOLEFINS, PASSING THE GASEOUS PRODUCT WITHOUT REDUCTION IN TEMPERATUREAND PRESSURE TO AN INTERMEDIATE POINT OF AN EXTRACTIVE DISTILLATIONZONE, INTRODUCING SUFFICIENT WATER TO THE EXTRACTIVE DISTILLATION ZONEAT A POINT SUBSTANTIALLY ABOVE THE GASEOUS PRODUCT FEED POINT TOMAINTAIN AN INTERNAL LIQUID REFLUX HAVING A WATER CONTENT OF 65-99.9 MOLPER CENT BELOW THE POINT OF ADDITION OF THE WATER, DISTILLING FROM THEGASEOUS PRODUCT UNDER SUBSTANTIALLY THE SAME TEMPERATURE AND PRESSURECONDITIONS OF THE HYDRATION REACTION A VAPOROUS MIXTURE COMPRISINGETHER, ALCOHOL AND UNREACTED OLEFINS WHICH FLOWS COUNTERCURRENT TO THEDESCENDING AQUEOUS REFLUX, AND WITHDRAWING AN AQUEOUS SOLUTION OFALCOHOL SUBSTANTIALLY FREE OF ETHER FROM A LOWER PORTION OF THEEXTRACTIVE DISTILLATION ZONE.